Blade protector for clearing machine

ABSTRACT

The invention relates to a cutter guard (13, 14) in clearing assemblies (1) provided with a cutter (3) mounted on a shaft (6) and rotatable by means of a motor (11), said shaft (6) being carried in a body (8), the guard comprising a hub section (13) provided in association with the cutter (3) and essentially coaxial with the shaft (6), the hub section (13) having a diameter which is less than the diameter of the rotatable cutter (3) and carrying a plurality of fixed arms (14) which extend outwards beyond the periphery of the cutter (3). The hub section (13) is arranged freely rotatable in relation to the body (8) and those parts of the arms (14) extending beyond the outermost periphery of the cutter (3) are provided with a surface facing in a direction opposite the rotational direction of the cutter (3) and extending up above the plane of the top surface of the cutter as well as to or below the plane of the bottom surface of the cutter (3), said arm surface having a radial extension arranged such that all tangents which can be drawn from the outermost periphery of the cutter between adjacent arms will cut that of the surfaces which is located on that of the two arms which lies rearmost, as viewed in the rotational direction of the cutter, the arms furthermore being formed such that radial movement along the surface of a particle or the like leaving the periphery of the cutter (3) tangentially and hitting the surface will be opposed.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a cutter guard in clearing assemblies which areprovided with a cutter mounted on a shaft and rotatable by means of amotor, the shaft being carried in a body. Such assemblies are oftenmounted on an implement arm or beam, e.g. on a forest machine, and usedfor clearing bushes and shrubbery.

BACKGROUND OF THE INVENTION

In clearing forest, clearing tools have previously been used whichnormally are mounted on a comparatively long, parallelly guided beam orjib mounted on a forest machine and swingable about its supporting pointon the machine. Furthermore, the beam can be moved outwardly from andinwardly towards the machine, in doing which the clearing tool at theend of the beam is maintained on a constant level thanks to the parallelguidance of the beam. The constant level can usually be adjusted. Asclearing tool a disc has been used, rotatably driven by a motor,pivotally secured knives or beaters being provided on the periphery ofsaid disc. The knives or beaters will reach a comparatively high speedon account of the large diameter and high rotational speed of the disc,usually about 1500 revolutions per minute (RPM). Moreover, as the knivesor beating tools have to be comparatively heavy in order to operate inthe desired manner their total kinetic energy will be high. If thebeaters strike objects as rocks and pieces of woods these couldtherefore be thrown far away from the assembly at a high speed, as it isalmost impossible to mount a completely covering guard around therotating disc because, if so, the beaters would not get in touch withthe vegetation to be cleared. This device thus requires a very greatsafety distance, up to 100 m. As the machine itself is of coursesituated within the safety distance the assembly must also be providedwith a guard on the side facing the operator, which means that theassembly only can clear when it is moved outwardly from the machine, orlaterally, which is a great disadvantage. A further disadvantage is thefact that it is hard to raise the RPM and thus the capacity of theassembly, as the beaters or knives can then be exposed to such largeforces that they may be torn loose. Hence, this previously used deviceis thus impaired by certain defects.

In an attempt to provide an assembly which is not defective in this wayit has been proposed to use a rotating cutter having saw teeth insteadof a rotating disc provided with beaters or knives. Such a structurewill eliminate in practice the risk of objects being through out fromthe assembly, which brings with it that the safety distance can bereduced to more normal values. However, the cutter must be protectedagainst contact with larger rocks and the like, as the cutter, incontrast to the pivotally mounted beaters or knives, does not yield uponcontact with solid objects. Thus one object of the invention is toprovide a guard for the cutter.

Some solutions of this problem can be found in, for example, U.S. Pat.Nos. 4,736,573, 2,532,982 and FR-A-1 548 806, according to which thecutter is protected by means of fixed arms extending radially from thecenter of the cutter. These known devices are intended, however, forlawn-mowing, hedge trimming etc. and the set of problems and technicalsolutions which form the basis of these previously known devices cannotquite simply be applied to assemblies for clearing forest, as theproperties of the types of vegetation concerned are essentially unlike,primarily with respect to size and resiliency, which makes the demandsupon the design of the equipment significantly different.

Moreover, in certain cases, above all when large cutters are concernedwhich rotate at a comparatively high RPM and/or cutters having a few,large, heavy teeth, it can also be desirable to prevent that objects,e.g. parts coming loose from the cutter, are thrown out from theclearing assembly.

A further object of the invention is thus to provide protective meansagainst objects being thrown out from the clearing assembly.

BASIC CONCEPT OF THE INVENTION

These objects are attained by means of a cutter guard comprising a hubsection of a diameter less than the diameter of the rotatable cutter,which guard is provided essentially coaxial with the axis of rotation ofthe cutter and is freely rotatably in relation to the cutter, a numberof fixed arms being secured to the hub section and extending outwardsbeyond the edge of the cutter.

Furthermore, those parts of the arms which are situated beyond theoutermost periphery of the cutter are provided with a surface facing ina direction opposite the rotational direction of the cutter andextending up above the plane of the top surface of the cutter as well asto and below the plane of the bottom surface of the cutter, said surfacehaving a radial extension selected such that all tangents which can bedrawn from the outermost periphery of the cutter between two adjacentarms will cut that of the surfaces which is located on that of the twoarms which lies rearmost as viewed in the rotational direction of thecutter. Furthermore, the arms are designed such that they will opposeradial movement along the plate of a particle or the like hitting theplate tangentially from the periphery of the cutter.

SHORT DESCRIPTION OF THE ANNEXED DRAWINGS

FIG. 1 shows a clearing assembly mounted on a parallelly guided cranebeam or jib.

FIG. 2 shows, in elevation, the clearing assembly disconnected from thecrane beam.

FIG. 3 shows, in plan, the guard proper, the position of the cutter inrelation to the guard being indicated by dashed lines.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 illustrates how the clearing assembly, here as a whole designated1, can be provided on a parallelly operated crane beam or jib,designated 2 in its entirety and mounted on a conventional forestmachine, not shown. As can be seen from the drawing the beam can beswung about a vertical axis 6 associated with the machine as well astowards and away from the machine. As a consequence of the parallelsteering of the beam the clearing assembly will follow, when movedoutwardly away from the machine or inwardly towards the machine, arectilinear path which can be adjusted parallel to the ground. The beamper se does not form any part of the invention and will therefore not bedisclosed in any detail here.

FIGS. 2 and 3 show the clearing assembly and the cutter blade guard ingreater detail. The cutter blade 3 is provided with saw teeth 4 and ismounted by means of bolts, not shown, on a rotatable shaft which iscarried in a body 8 by means of antifriction bearings. The body 8comprises a pair of parts 9', 9" which extend upwardly and are pivotedat their upper ends to the end of the beam 2. Between the body 8 and thecrane beam 2 also a hydraulic cylinder 10 extends for the angularadjustment of the clearing assembly. Between the two body parts 9, 9" ahydraulic motor 11 is provided which drives the cutter blade 3 by way ofthe rotatable shaft. Feeding of the hydraulic motor 11 is carried out inthe usual way by means of hydraulic conduits, not shown here. The body 8also comprises a downwardly projecting part 12 wherein bearing means areprovided for supporting the rotatable shaft. A hub section 13 isprovided on the outside of this projecting part 12, freely rotatablethereon. The hub section 13 has a diameter less than the diameter of thecutter blade. On the hub section 13 a plurality of fixed arms 14 aresecured which are spaced evenly along the periphery of the hub section,thus at the same angular distance from each other. The arms extendbeyond the periphery of the cutter blade.

Those parts of the arms 14 which extend beyond the cutter 3 are formedas surfaces or plates 16 oriented essentially perpendicular to the planeof the cutter 3. The plates 16 extend up above the plane of the top sideof the cutter 3 and to or below the plane of the bottom side of thecutter. Where the plates extend below the cutter 3 they will alsoprotect the cutter 3 from contacting the ground. The radial extension ofthe plates 16 is selected such that all tangents which can be drawn fromthe outermost periphery of the cutter between two adjacent arms 14 willcut the plate 16 on that of the two arms 14 which is located rearmost,as viewed in the rotational direction of the cutter, that is, so that aparticle or fragment which comes loose or is thrown out from theperiphery of the cutter 3 and thus is ejected along a tangential path,will hit the plate 16. As the hub section 13, upon which the arms 14 aresecured, is rotatably carried in the body, said plate 16, havingtogether with the hub portion 13 and the rest of the arms 14 acomparatively large mass, will yield in the rotational direction 15 ofthe cutter 3, thereby absorbing substantially the whole kinetic energyfrom the particle or fragment.

This means that the particle will be slowed down and fall to the groundinstead of being ejected at high speed from the clearing assembly.

By the outermost periphery of the cutter 3 it is here aimed at thecircular orbit of the point or points which are located outermost on thecutter 3, as measured from the centre of the cutter.

Furthermore, the plate 16 is formed in order to counteract movementradially along the plate of a particle or fragment which is throwntangentially by the cutter towards the plate. In the present, preferredembodiment the plate is formed such that its outer half 17 is bentbackwards, against the rotational direction of the cutter, so that theouter angle formed between the outermost tangent possible to draw fromthe periphery of the cutter between the two arms and the outer half 17of the plate 16 will be 90° or less.

In the ideal case however, the plate is curved in such a way that alltangents which can be drawn from the periphery of the cutter 3 in therotational direction between two arms 14 will kit the plate 16 at rightangle, that is, the plate 16 is curved as an involute of the outermostcircular periphery of the cutter, to the effect that the particle willnot obtain any component of movement directed along the plate. As amatter of course the plate 16 can also be provided with traversingflanges or the like, which are essentially perpendicular to the plane ofthe cutter and will prevent a particle from sliding outwards along theplate or from bouncing outwardly. It is also conceivable that the platebe formed so as to exhibit a high friction on the side facing in thedirection opposite the rotational direction of the cutter.

Also, as seen in the figure the number of arms can be selectedcomparatively great and in the preferred embodiment, such as illustratedin the annexed drawings, the number of arms has been selected fifteen.This means that the tangents which are directed in the rotationaldirection of the cutter will hit the plate 16 at an angle only verylittle deviating from 90°, which means, in principle, that the risk issmall that a particle or fragment, travelling of course in the directionof these tangents, will bounce outwardly from the cutter guard, as theparticle also in this case will obtain a very small component ofmovement directed along the plate 16. That this solution is conceivableis due to the fact that the diameter of the trees etc. to be clearednormally is comparatively small as compared with the effective diameterof the clearing assembly.

As shown in FIG. 2 the cutter guard is advantageously arranged such thatit slopes somewhat downwards from the center of the hub section in orderthat chips, twigs etc. falling upon the guard will slide down and falloff therefrom.

The part of the lower edge of the arms 14 located above the cutter 3 isparallel thereto and lies comparatively close to the cutter. This willreduce the risk of chips, twigs or the like getting caught between thearms 14 and the cutter 3.

The direction of rotation is indicated by the arrow 15 in FIG. 3. Thedistance between the arms 14 is selected such that it allows thevegetation to be cleared to enter and reach the cutter between twoadjacent arms and to be able to reach all the way to the hub section 13.Suitably the hub section is semi-circularly recessed between twoadjacent arms 14. At the same time the distance between two adjacentarms is also selected such that larger stones or rocks, and also largertrees which should not be hurt by the cutter, cannot reach so far inbetween two adjacent arms that they will contact the cutter. Here it maybe pointed out that on the level where the clearing assembly is normallymoving over the ground when clearing there are seldom rocks or similaritems which are so narrow that they correspond to the thickness ofvegetation ready for clearing. If any of the arms should hit straightly,for example, a small tree to be cleared, the whole guard can yieldthanks to the fact that the hub section 13 is rotatably carried in thebody part 8. This process is facilitated if the outer portions of thearms are bent laterally somewhat, for instance as shown in the preferredembodiment discussed above.

Thanks to the symmetrical structure of the cutter guard the cutter canoperate without limitation in all directions of movements parallel tothe ground. As the risk of particles being thrown out from the cutter issmall, no specific guard is necessary on the side of the clearingassembly facing the machine. The cutter in combination with the cutterguard will thus offer a very simple and effective solution of theproblems which up to now have been inherent in devices for mechanicalclearing. In principle the rotational speed of the cutter is not limitedupwards (or downwards) but can be selected freely according tocircumstances prevailing. A usual speed is about 2200 revolutions perminute (RPM).

CONCEIVABLE MODIFICATIONS OF THE INVENTION

As a matter of course the invention can be modified in many other wayswithin the scoope of the accompanying patent claims. As for example, theassembly can be mounted on a beam or jib of optional type. Furthermore,any kind of motor can be used for driving the cutter. The motor used cane.g. be driven by gasoline or be operated hydraulically, electrically,pneumatically or in some other suitable way. Neither is it necessary toarrange the motor in direct connection with the cutter. The cutter usedcan of course be of any suitable type. In principle it is alsoconceiveable that the cutter guard be used in the type of cutterdiscussed initially and which comprises a rotating disc with beaterspivotally secured along the periphery. As these beaters must have acomparatively large mass in order to operate as intended, however, inthis case heavy demands will be made upon the design and dimensioning ofthe guard.

Furthermore, it should be pointed out here that with respect to themethods discussed above for designing the arms 14 so as to opposemovement along the arm surface of a particle hitting the surface, thesemethods can be optionally combined except for the case where the surfacehas been bent, which case of course cannot be combined with the casewhere the surface has been formed as an involute.

We claim:
 1. In a clearing tool assembly provided with a circular cuttermounted on a shaft and rotatable in one direction by means of a motor,the shaft being carried in a body, a cutter guard comprising a hubsection located substantially coaxially with the shaft and located abovethe cutter, said hub section having a diameter which is less than thediameter of the cutter and carrying a plurality of arms which extendradially outwards beyond the periphery of the cutter, and wherein saidhub section is arranged freely rotatable in relation to the body andwherein portions of the arms which extend beyond the outermost peripheryof the cutter are each provided with a surface facing in a directionopposite the one direction and extending up above a plane containing atop surface of the cutter as well as to or below a plane containing abottom surface of the cutter, each said arm surface having a radialextension arranged such that all tangents which can be drawn from anoutermost periphery of the cutter between two adjacent of said arms willintersect that arm surface of said two adjacent arms which liesrearmost, as viewed in the rotational direction of the cutter, each ofsaid arms further being formed such that radial movement of a particlealong a respective arm surface leaving the periphery of the cuttertangentially will be opposed by said respective arm surface.
 2. Thecutter guard according to claim 1, wherein said arm surface is one faceof a plate which is formed integral with the respective arms.
 3. Thecutter guard according to claim 1, wherein an outer half of the plate isbent backwards, opposite said one direction of the cutter in such a waythat the outer angle formed between the outermost tangent which can bedrawn from the periphery of the cutter between said two adjacent armsand the part of the outer half (17) of the plate (16) which lies outsidesaid tangent is 90° or less.
 4. A cutter guard according to claim 1,wherein each said surface is curved as the involute of the outermost,circular periphery of the cutter.
 5. A cutter guard according to claim 1wherein the number of arms is between 14 and 16.